Every Mac on the SAN needs a FibreChannel card, two GigE network interfaces, and Xsan software.
The RAID devices you use should have FibreChannel connections. Most will have ethernet connections for management. I don't know how caldigit.com's storage devices work, but I'd triple-check to be sure they can be used as Xsan storage devices.
All of the FibreChannel connections (from the Macs and the RAID devices) are linked together using a FibreChannel switch.
You need a GigE network, separate from your office LAN, that connects all of the Macs using their second GigE network interface. You'll configure Xsan to use that network for metadata.
At least two of the Macs should be configured as Xsan metadata controllers. The primary metadata controller (and optimally the secondary metadata controller) should be dedicated to the task. The metadata controller is the "traffic cop" for every bit of I/O on the SAN, so you don't want to bog it down with any other processes; otherwise your SAN performance will suffer.
I usually configure all the other Macs on the SAN as secondary metadata controllers. Previous versions of Xsan wouldn't allow you to manually choose which GigE network to use for metadata unless the workstation was configured as a controller. They've probably fixed that issue by now, but I'm still into redundancy. It doesn't hurt anything.
